The invention relates generally to devices for shifting clutches in motor vehicle drive line components and more specifically to an integrated unit having a shift motor and electronic controller disposed in housing.
Selection of gear or speed ranges in motor vehicle components such as automatic transmissions and transfer cases takes many forms. In automatic transmissions, pressure sensors, hydraulic actuators and band clutches achieve shifts according to carefully developed programs relating to speed, acceleration and other variables. Gear selection in motor vehicle transfer cases is typically made by the vehicle operator and thus the devices tend to be less complex and include a hydraulic or electric operator coupled through a suitable linkage to a shift fork which moves a multiple position clutch member. Various sensors may be disposed on or adjacent the moving components to provide feedback to a controller to indicate the position of the clutch member.
Certain operational conditions present difficulties with such shift arrangements. When transferring large torque loads, the circumferential forces on gear teeth may render it difficult or impossible to disengage the gear teeth until such torque loads are reduced. Such a condition is often referred to as torque block. A comparable problem on engagement stems from a different situation. During attempted engagement, if the faces of the gear teeth clash, engagement will likewise be difficult or impossible. This condition is often referred to as spline block. Both of these conditions result in the inability to complete a directed or commanded shift.
How the shift linkage resolves these conditions has been addressed in many ways. One of the more common solutions is to provide an energy storing and force generating device such as a spring between the operator and the clutch. When torque block or spline block is encountered, the operator, typically an electric motor, moves to its final position, the spring stores energy and the shift is completed when the shift inhibiting condition abates. This solution, however, may require motors of a larger size than would otherwise be necessary, motors capable of being safely stalled and may create operational anomalies if the shift is delayed for a relatively long period of time.
Another issue with prior art shift control assemblies relates to the operating environment. Typically, an electric drive motor is mounted on the outside of a transfer case and coupled to a clutch through a shift linkage. Sensors, often disposed within the transfer case, provide information regarding the current status of the shift linkage to a remotely mounted controller through cables and connectors and the controller provides drive signals to the electric shift motor, again through cables and connectors. The separation of these components and their interconnection through cables and connectors, which facilitate installation and service, occasionally are the source of operating anomalies.
The invention herein disclosed and claimed addresses these and many other design issues.